Reciprocating electromagnetic mechanism



Aug. 17, 1965 E. B. MYERS RECIPROCATING ELECTROMAGNETIC MECHANISM 2 Sheets-Sheet 1 Filed May 24, 1962 Yoatb J0@ INVENTOR. El-MAN B. Mmes WW Aug. 17, 1965 E. B. MYERS RECIPROCATING ELECTROMAGNETIC MECHANISM 2 Sheets-Sheet 2 Filed May 24, 1962 INVENTOR. [wmv B M yf'es BY ,4 TrolQ/YEY .TWLI

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United States Patent O 3,201,67t RECIPRCATENG ELECTRGMAGNETIC MECHANESM Elman B. Myers, Wayne, NJ., assigner to Fuller-Myers, Spokane, Wash., a partnership composed oi Cecil R. Fuller, Spokane, Wash., and Elman E. Myers, Wayne,

Filed May 24, 1962, Ser. No. 197,535 4 Claims. (Cl. S18-125) This application is a continuation-in-part of my copending application Serial No. 28,489, tiled May 1l, 1960, and entitled Pulse-Excited Electromagnetic System, now abandoned.

This invention relates generally to electromagnetic driving mechanisms, and more particularly to an electrically-energized reciprocating mechanism intended to be held by a user to drive an appliance such yas a razor or toothbrush,the mechanism being light-weight, eiiicient and safe to hold.

There are many tools and other instrurnents which are manipulated by the user` and are driven by a motor or drive mechanism clasped by the hand of the user. Thus electrically-operated saws, sanders, razors and toothbrushes are examples of reciprocating appliances which are held and directed by a user. The fact that fthe drive mechanism is to be held imposes certain requirements thereon which are of great importance in determining the practicality of the device. The drive mechanism must be relatively light and compact, and yet highly eflicient in order to perform effectively. At the same time, the mechanism must function without producing excessive and uncomfortable amoun-ts of heat, and the user must be protected against electrical shock. With these factors in mind, we shall now consider existing drive mechanisms.

One known method of producing reciprocal motion electrically is by the use of a tractive electromagnetic device or solenoid energized by `alternating current and including an armature which is caused to reciprocate in accordance with the applied current. Alternating-current electromagnets suier from a number oi serious drawbacks, as compared to direct-current devices. They are limited in force, in that for a given pole face area the average force on alternating-current is only half that obtained with direct current. They need more iron to develop the same force and more copper to carry the large reactive power for A.C. operation, and this adds to the weight of the device.

In addition to hysteresis losses, another `serious limitation in A.C. electromagnetic devices arises from eddy current losses. These currents are produced by voltages induced in the iron by the alternating or pulsating magnetic eld passing therethrough. Such losses result in heating, and make the device uncomfortable to handle.

To avoid the drawbacks incident to alternating-current electromagnetically-operated reciprocating drives, attempts have .been made to obtain the same action with direct-current solenoids. In order to energize the solenoids so as to produce a reciprocal action, it has been known to make use of microswitches to break the circuit periodically. lt has also been known to use reotiers in conjunction with A.C. sources for the same purpose. It has been found, however, that even with such expedients, a high degree of heat is developed.

Wherethe reciprocating device is to be held in the hand of the user, as for example in the case of an electrically driven razor, the generation of heat, apart from its effect on the eiiiciency of the drive, makes it diiiicult to handle the razor. Experience has shown that some electric razors become so hot when in use for more than a few minutes as to make shaving almost impossible. The reason heat is generated in a tractive electromagnet lice arises from the fact that once the input energy has been converted into work or movement of the armature, the remaining power, as in the case of a stalled motor, is dissipated as heat.

Another factor which is of vital concern in electrically-operated devices held by the user, is safety from LlO ' shock. Since in the case of an electric toothbrush the brush is placed under the water faucet to be made wet or cleaned, any electrical leakage in this device may havel dangerous consequences. Sealing however is ditiicult to eifect in a device in which the appliance is coupled to a plunger which lreciprocates within an electrically energized solenoid.

in View of the foregoing, it is the principal object of the present invention to provide an electromagnetic device capable of producing reciprocal motion, which operates efficiently and at relatively low temperatures, and which provides a high measure of security from electrical shock.

More particularly it is an object of the invention to provide an electromagnetic drive system including directcurrent solenoids operating in conjunction with an alternating current diode switching circuit wherein the solenoids are operated by periodic pulses to convert the input energy into work and to minimize heat dissipation, the arrangement being such that for each cycle of the applied alternating current, an armature is pulled in one direction and then in the opposite direction, whereby the. armature is bi-pulsed.

A feature of the invention resides in the use of an elastic oscillator in conjunction with the reciprocating armature, which acts to render the system mechanically resonant and rsynchronous with the line current and yet to limit the operating stroke.

. Another object of the invention is to provide a compact, sealed and'highly erhcient and light-weight electromagnetic driver adapted to produce reciprocating motion with ,relatively mechanism being electrically isolated from the user.

Another feature of the invention resides in the use of porous pole pieces for the electromagnetic device, which ieces function also as lubricated bearings for the reciprocating armature.

Still another object of the invention is to provide a bi-pulsed reciprocating mechanism constituted by two sets of solenoids in axial aligment, each set being composed of a pair of bi-iilar windings to create a uniform distribution of lield energy.

For a better understanding of the invention as well as other objects and features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawings, wherein:

FIG. l is a schematic diagram of the magnetic circuit of the electromagnetic drive mechanism and the associated diode circuit in accordance with the invention;

FIG. 2 is a longitudinal section taken through the structure of the drive mechanism;

FIG. 3 is a wave form of the applied voltage and indicating the resultan-t diode and coil circuit operation;

FIG. 4 separately shows the plunger of the mechanism;

FIG. 5 is a longitudinal section through fthe rear pole piece;

FIG. 6 is an end view of the rear pole piece; and

FIG. 7 is an end View of the center pole piece.

Referring now to FIG. 1, the magnetic circuit of the mechanism is constituted by a cylindrical casing lil, within which is coaxially disposed a reciprocating plunger 1l, the plunger being operative with respect to three pole pieces consisting of a center or bi-pole piece 12, having an annular form, and a pair of end pole pieces, 13 being the front piece and 14 the rear piece. These components `are all of ferromagnetic materials of high permeability.

Plunger 11 is in rolling pin form, the ends thereof great force and relatively little heat, the n the usual 110 volts of alternating current;

tapering to provide truncated cones which terminate in smaller cylindrical plugs 11a and 11b. Attached to plug 11a is a d-rive shaft 15 which terminates in a chuck 16 or other clamping device, for coupling the plunger to an appliance such as a toothbrush. p

The diameter of the borein central pole piece 12 is such as to permit the free movement of theplunger 11. The bores in the end pole pieces 13 and 14 are formed with a truncated conical section to accommodate the tapering end portions of the plunger and to limit the stroke thereof and a cylindrical section to accommodate plugs 11a and 11b. Y

Fitted over plugs 11a and 11b and bonded thereto are conductive tubes 18 and 19 each of whichV constitutes a single-turn shading coil. Disposed in the front section of the structure surrounding plunger 11, in the annular area between the center pole 12 and the front pole 13, are a pair of bi-iilar wound coils A and B, while in the rear section between the center pole and the rear pole 14, are a second pair of bi-lilar wound coils C and D, all of the coils having the same number of turns. v

The coils are energized through a diode bridge circuit formed by four identical diodes D1, D2, D3 and D4, which may be installed and potted within a male electrical plug Ztl to be inserted in a power outlet providing The diodes are preferably of the semi-conductive silicon type having low reverse leakage. The diodes act as unidirectional switching and current limiting elements.

Prong X of the plug 20 is connected seriatim through diode D1, in the forward direction, and cable lead a through coil A in series with coil B, lead b and diode D2, alsol in the forward direction, to the second prong Y. Prong Y is connected seriatirn through diode D3 in the forward direction and cable lead c through coil C in series with coil D, lead d and diode D4 in the forward direction to prong X. v

The diodes are unidirectional devices and hence conduct only in the forward direction. Thus, as indicated in FIG. 2, during the positive half-cycle of the alternating current, current tlows only through the front coils A and B, diodes D1 and D2 being then conductive and diodes D3 land D4 being inoperative, since they are in the reverse direction relative to the applied polar-ity. In the negative half-cycle, current llows only through the rear coils C and D, diodes D3 and D., then being conductive and diodes D1 and D2 being inoperative.

It will be seen, therefore, that two distinct magnetic circuits are provided. The irst is a front circuit through the front half section of the plunger 11, the center pole 12, the front half of casing 10, and the front pole piece 13, the space between the tapered portion of the plunger and the conical section of the front pole piece constituthigh-voltage surge which substantially exceeds the line voltage. During the negative half-cycles, a similar voltage peak occurs with respect to the action of diodes D3 and D4 and coils C and D.

As pointed out previously, heat is dissipated by the solenoid mainly after work has been carried out. By reason of the sharp peaking action, the energy level is greatest at the outset of the plunger stroke to overcome.

the initial inertia when reversing the stroke direction. The current ow is then limited by the diode operation and drops sharply to minimize heat dissipation subsequent to the completion of work.

It will be observed that symmetrical loads are imposed on the power supply during alternate half-cycles to prof the coils increase in resistance, thereby reducing current iiow and producing lower forces. In the present invention, even though current ow exceeds normal levels during the work period, the arrangement is such that the temperature goes up only slightly above ambient and the eiiiciency of the device is far superior to conventioning an air gap. The second is made up of the rear half Y i of the plunger, center pole 12, the rear half of casing 1t) and rear pole piece 14. Thus center pole 12 is common to both magnetic circuits, and at the same time it shields the active magnetic circuit rfrom the inactive one,

During the iirst half-cycle of the applied current, the bi-lar wound coils A and B are concurrently energized in the same sense to activate the front magnetic circuit and pull plunger 11 in the forward direction, while during the second half-cycle coil-s C and D are concurrently energized in the same sense to activate the rear magnetic circuit and to pull plunger 11 in the opposing direction. This pull-reverse pull or bi-pulsed action provides the forwardand reverse stroke of the driver, there being. no need for springs or other bias means to effect a return stroke.

During the positive half-cycle of the alternating wave, the current is switched by diodes D1 and D2 through serially connected coils A and B, and because of the high inductive reactance of the circuit, shock excitation occurs when the diode'switches are actuated, thereby tending toward a damped oscillation giving rise to a-sharp and very ally operated D.C. solenoids.

The shading coils 18 and 19 constitute single-turn coils which enclose only a portion of the total flux passing through the plunger. Because of the leakage reactance 0f this turn, the current induced in it is out of phase with the inducing `flux, hence at the moment when the inducing flux due to the main winding (A and B or C and D) is zero, current in the shading coil still persists and produces a fnishingfpull. This effect augments the maximum pull for a given impressed EMF, for the maximum pull is the vector resultant of the main and local lluxes. The bi-ilar arrangement acts to produce a uniform distribution of eld energy, thus further enhancing the efficiency of the instrument.

Referring new to FIG. 3, an actual embodiment of the invention is disclosed based on the operating principles described in connection with FIG. Vl. The cylindrical casing 10, which forms part of the magnetic circuit, is preferably fabricated of low carbon steel or other suitable ferromagnetic material of high permeability. The casing is housed within a plastic insulating shell 21, whose front end is open to provide access to the tool or appliance clamping chuck 16 which is composed of spring lingers or other clamping means, and is connected by shaft 15 of stainless steel to plunger 11. The rear end of shell 21 is enclosed by a plastic cap 22 which is cemented thereto as by an epoxy or a suitable plastic solvent, such as ethylene dichloride for a Lucite plastic. Projecting from cap 22 and cemented thereto, is a rubber grommet 23, the

four cable leads a, b, c and d passing through the grommet into a cable 24, preferably sheathed by braided copper and covered with a vinyl plastic tube to provide a lightweight cable cord of high electrical and mechanical strength as well as liexibility.

The three pole pieces 12, 13 and 14 are supported within casing 1t) on a stainless steel bobbin 28, the center pole piece 12 being received over the bobbin, and the front and rear pieces 13 and 14 being telescoped within the ends of the bobbin as by push-litting. All of the pole pieces are fabricated of iron powder by powder metallurgical techniques, the powder being initially cold-compacted to shape, then sintered to consolidate the particles, and nally coined or otherwise machined to the nal size.

The end pole pieces are not compacted to full density but are deliberately made porous as in the case of con- Ventional machine bearings to act not only as pole pieces, but as lubricated shaft bearings. For this purpose, the

pole piece pores are saturated in an oil of a suitable Viscosity and quality such as turbine oil whereby the bearingsremain lubricated for the'entire life of the driver unit.

The single-turn shading coils are preferably formed of pure oxygen-free copper tubes which are forced over or bondedl to the end plugs 11a and 11b of the plunger, and are polished or chromium-plated, since they act as a friction bearing surface with respect to the lubricated, porous iron end pole pieces. `It is magnetically desirable to have the plugs lit exactly into the pole pieces to provide a tight magnetic coupling with zero air gap.

The front end of the driver is sealed by means of an annular disc 25 which may be formed or brass-plated powdered iron. The disc is securely attached, as by epoxy cement, or by grooved pins, to the end of front pole piece 13, the disc being provided with a central collar 25a. Received over the collar 25a and vulcanized thereto is one end of flexible tube 260i rubber or other elastic material, the other end of the tube being vulcanized to a second disc 27 cemented to the base of chuck 16. Thus the rubber tube and its associated discs hermetically seal the front end of the driver. The chuck 16 is preferably formed of a suitable high-strength, resilient plastic such as reinforced nylon, and is adapted to engage a suitably designed appliance handle for a toothbrush T or other device to be reciprocally driven.

The rubber tube 26 in conjunction with the reciprocating plunger constitute a mechanical resonator which is actuated in both directions, the rubber serving not only to seal hermetically the front end of the driver, but also to limit the reciprocating stroke. The elastic stretching and compression characteristics of the rubber tube, coupled with the reciprocal mass and force momentum of the plunger and the parts associated therewith, interlock the mechanical movement to the power line frequency, thereby creating a synchronous device.

Received over the steel bobbin 28 are a pair of insulating bobbins 29 and 30, preferably formed of a thermosetting plastic bobbin 29 supportion the bi-lar wound front coils A and B between the center pole piece and the front pole piece, and bobbin 30 supporting the rear bitilar wound coils C and D.

As best seen in FIGS. 5 and 6, the rear pole piece 14 is provided with four equi-spaced peripheral slots 14a to allow for the passage of the cable-connecting leads a, b, c and d. Similarly, as shown in FIG. 7, the center pole piece 12 is also provided with slots 12a to permit passage of the leads to the front coils A and B.l

It will be evident that the coils are securely sealed electrically and mechanically within the housing of the driver unit and that water or any other iiuid or paste is incapable of making contact therewith. The cable wires which connect the driver coils to the rectifying diodes in the A.C. line plug 20, carry only D.C. current, and no A.C. centers the unit. The coils in the bridge circuit act also as voltage dividers, each carrying one half the applied voltage, which in ordinary practice would be 55 volts D.C. Thus a user placing the driver under water, as would be the case should the driver be coupled to a toothbrush, is in no danger of serious electrical shock, first because the unit is sealed and cannot be penetrated by conductive water, and second, even if such penetration were to occur, the voltages of the unit arehalved to a considerably less dangerous level.

In summary, the unit is constituted by a pair of axiallyaligned magnetic circuits in which the center pole piece is common to both circuits, the magnetic circuits acting upon an axial plunger to reciprocate the same by a bipulse action in which the plunger is alternately pulled in opposing directions. The juxtaposition of the truncated conical ends of the plunger to the conical pole pieces, and the tight coupling between the cylindrical end plugs of the plunger with the pole pieces, maximizes the axial forces obtainable.

No attempt has been made in the design disclosed lates about its longitudinal axis. This dual action is useful in the case of a toothbrush, for it provides a desirable dental cleaning motion which acts to massage the gum line as well as to clean the tooth surfaces. It is of course possible mechanically to prevent or limit such oscillations in other applications.

While there has been shown what is considered to be a preferred embodiment of the invention, it is to be understood that many changes may be made therein without departing from the essential spirit thereof as defined in the annexed claims.

I claim:

1. An electromagnetic drive unit comprising a pair of magnetic circuits in axial alignment constituted by a tubular casing having annular front and rear pole pieces enclosing the ends thereof and an annular pole piece disposed centrally therein, and a plunger coaxially disposed within said casing and extending through said centr-al pol-e piece, said plunger being reciprocable relative to the front and rear pole pieces and having ends slidable therein, said front and rear pole pieces being formed of sintered, porous iron members containing .a lubricant, a first winding surrounding said plunger in the area between said center piece and said front piece, a second winding surrounding said plunger in the area between the front piece and said rear piece, means alternately energizing said first and second windings with unidirectional current to lalternately pull said plunger in opposing directions, a shaft connected to the front end of said plunger and extending axially therefrom to engage an operating element, and an elastic tube surrounding said shaft, said tube being sealed at one end to said front pole and at the other end to said shaft.

2. An electromagnetic drive system comprising la pair of magnetic circuits in axial alignment constituted by a tubular casing having annular front and rear pole pieces enclosing the ends thereof and an annular pole piece disposed centrally therein, and a plunger coaxially disposed within said casing and extending through said central Vpole piece, said plunger being reciprocable relative -to the front and rear pole pieces, av first winding surrounding said plunger in the area between said center piece and said front piece, `a second Winding surrounding said plunger in the area between the front piece and said rear piece, each of said windings being constituted by a pair of bi-iilar wound coils, connected in series in the same sense, and means alternately energizing said first and second windings with unidirectional current to alternately pull said plunger in opposing directions.

3. A unit as set forth in claim 2, wherein said energizing means includes four diodes, two of which are connected in the same direction at either end of said seriesconnected coils of the first winding, the other two being connected in the reverse direction at either end of said series connected coils of the second winding.

4. An electromagnetic drive unit comprising a pair of magnetic circuits in axial alignment constituted by a tubular ferromagnetic casing having annular front land rear pole pieces enclosing the ends thereof and an annular pole piece disposed centrally therein, and a ferromagnetic plunger coaxially disposed within said casing and extending through said central pole piece, said plunger being reciprocable relative to the front and rear pole pieces, and having ends slidable therein, said front and rear pole pieces being formed of sintered, porous iron members containing a lubricant, a first winding surrounding said plunger in the area between said center piece and said front piece, and a second winding surrounding said plunger in the area between the front piece and said rear piece, and metallic tubes of non-magnetic material fitted over the ends of said plunger and slidable in said front and rear pole pieces to maintain a magnetici gap between said plunger and said front and rear pole pieces.

References Cited bythe Examinerl UNITED STATES PATENTS Fleischer et a1. 310-29 Daniels 310-f29 Burgess 321-8 Weyandt B18-125 Daniels et a1. 308-240 Wohl 310-2-9 Hartwig 320-2 MILTON O. HRSHFIELD, Primary Examiner. 

2. AN ELECTROMAGNETIC DRIVE SYSTEM COMPRISING A PAIR OF MAGNETIC CIRCUITS IN AXIAL ALIGNMENT CONSTITUTED BY A TUBULAR CASING HAVING ANNULAR FRONT AND REAR POLE PIECES ENCLOSING THE ENDS THEREOF AND AN ANNULAR POLE PIECE DISPOSED CENTRALLY THEREIN, AND A PLUNGER COAXIALLY DISPOSED WITHIN SAID CASING AND EXTENDING THROUGH SAID CENTRAL POLE PIECE, SAID PLUNGER BEING RECIPROCABLE RELATIVE TO THE FRONT AND REAR POLE PIEES, A FIRST WINDING SURROUNDING SAID PLUNER IN THE AREA BETWEEN SAID CENTER PIECE AND SAID FRONT PIECE, A SECOND WINDING SURROUNDING SAID PLUNGER IN THE AREA BETWEEN THE FRONT PIECE AND SAID REAR PIECE, EACH OF SAID WINDINGS BEING CONSTITUTED BY A 